I'm not sure that your comment is responsive to the original post. FSRM is fast on Intel, even with single byte strings. AMD claims to support FSRM with recent

I'm not sure that your comment is responsive to the original post. FSRM is fast on Intel, even with single byte strings. AMD claims to support FSRM with recent CPUs but performs poorly on small strings, so code which Just Works on Intel has a performance regression when running on AMD. Now here you're saying `REP MOVSB` shouldn't be used on AMD with small strings. In that case, AMD CPUs shouldn't advertise FSRM. As long as they're advertising it, it shouldn't perform worse than the alternative. https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/2030515 https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/2030515 https://sourceware.org/bugzilla/show_bug.cgi?id=30994 https://sourceware.org/bugzilla/show_bug.cgi?id=30994 I'm not a CPU expert so perhaps I'm misinterpreting you and we're talking past each other. If so, please clarify.